Intrusion detecting apparatus and method

ABSTRACT

An apparatus and a method for detecting motion in a given space, operable to produce an image of said space upon a retina of photoconductive cells, which produce alternating changes in conductivity of the cells and alternating changes in voltage at the output of said cells in response to changes in the image of said space and wherein the alternating voltage changes are processed to select those signals which are attributable to the motion of an intruder in said space, to selectively amplify them, to discard those voltages of low amplitude below a predetermined level, to convert the voltage changes above the predetermined amplitude level into pulses of uniform amplitude and width, to produce a voltage dependent on the pulse rate of said pulses above a predetermined pulse rate for triggering an alarm signal for indicating intrusion.

United States Patent 1 Campman 1451 Dec. 25, 1973 INTRUSION DETECTINGAPPARATUS AND METHOD Primary Examiner--J0hn W. Caldwell AssistantExaminer-Glen R, Swann, Ill [75] Inventor. {jams P. Campman, S1lverSpnng, Atmmey Jack H. Unseen [73] Assignee: Vidar Laboratories Inc.,[57] ABSTRACT Kensmgton An apparatus and a method for detecting motionin a 2 Filed; Apt 27 972 given space, operable to produce an image ofsaid space upon a retina of photoconductive cells, which [21] APPI- N04248,211 produce alternating changes in conductivity of the cells andalternating changes in voltage at the output 52 us. c1. 340/258 B,250/209, 250/221, of Said cells in response to Changes in the image of 30 7 said space and wherein the alternating voltage changes 51 1m. (:1.G08b 13 18 are Processed to Select those Signals which are attrib- [58]Field of Search 340/258 B, 228 s, table to the motion of an intruder inSaid Space, to 340/227 R, 27 25 250 210 X, 210 209 selectively amplifythem, to discard those voltages of X, 209 2 1 x 2 low amplitude below apredetermined level, to convert the voltage changes above thepredetermined ampli- 5 References Cited tude level into pulses ofuniform amplitude and width, UNITED STATES PATENTS to produce a voltagedependent on the pulse rate of said pulses above a predetermined pulserate for triggiifigz g gering an alarm signal for indicating intrusion.3:309:689 3/1967 Keeney 340/258 B 8 Claims, 10 Drawing Figures 6 9 JIMPEDANCE ----F T 3 LIGHT LEVEL F'LTER TRANSFORMER SEN 5IT|VE DETECTORFILTER AMPLIFIER AMPLIFIER STORAGE AMPLITUDE BLEED NORMALIZER SWITCHALARM I? ltfpllS I4 13 PULSE WIDTH NORMALIZER PAIENTEU 3.781.842

SHEET 1 BF 4 6 'MPEDANCE LIGHT LEVEL F|| TER TRANSFORMER SENSITWE(DETECTOR I 2 3 4 5 8 I0 ll FILTER AMPLIFIER AMPLIFIER STORAGE AMPLITUDEBLEED SWITCH 7 NORMALIZER F|G.l |l i ALARM I? |6\l5 l4 l3 PULSE WIDTHNORMALIZER PATENTEDUECZS I973 SHEEI 2 BF 4 FIG.3

FIG. 4

INTRUSION DETECTING APPARATUS AND METHOD SUMMARY OF INVENTION Thepresent invention relates to an apparatus that has for its purpose theof viewing a specific area or space, enclosed or unenclosed, to detectthe entrance of an intruder, to sound an alarm or provide an indicationof the entrance of the intruder, to detect motion in the area or spaceand to modulate the alarm or indication at a rate determined by the rateof movement of the intruder in the area or space.

There are problems involved in accomplishing such a purpose. One problemis that such apparatus is subject to tampering to render themineffective in carrying out their purpose. Another problem, and possiblythe mostworrisome one, is that of false alarms, that constitutes one ofthe factors of the unreliability of the apparatus. Still another problemarises from dependence on commercial power sources to power theapparatus, the failure of which renders the apparatus ineffective, andthe variations of which often results in false alarms.

Such apparatus has been complex and costly to install and maintain andbeyond the reach of the average home owner, business man and smallwidespread operator. As a consequence, the apparatus has not foundwidwspread acceptance as a deterrent against house breaking andburglary.

One of the chief causes of false alarms have been the entrance upon thespace, from the outside, of influences that are normal to the spacesurrounding the space being monitored. In the particular art to whichthe present invention belongs, it has been reflections of light patternsthat have motion across the monitored area, or the intrusion of a changein light intensity that illuminates a portion of the total areamonitored, relative to other portions of the area. This causes signalvoltages'to be generated in the apparatus, and unless removed, willcause an alarm. Such moving light patterns would be, for example, likethose produced by a passing vehicle that either shines its own lightsinto the monitored space, or causes light to be reflected from the glassor chrome trim. A flashing light that changes the intensity of light onone portion of the area monitored would be exemplified by the outsidesign lamps shining through a window viewed by the apparatus, orlightning flashes, or the passing of a cloud that would darken thewindow. These are but a few of the causes of false alarms.

There have been attempts made in the past, to eliminate the many causesof false alarms, which, while at least partially successful, haveintroduced other problems.

One such arrangement has been to use infra-red light means to flood thearea to be monitored, and making the receiver or detector responsiveonly to infra-red light. Similarly, artificial light is used andmodulated at a predetermined rate or frequency and the detector is tunedto receive the frequency of the illumination. Such methods of overcomingthe problem of false alarms have been costly, to install, and to operateand have involved extensive changes in the wiring system. hey alsoprovide a handy means by which the potential intruder might render thedetector apparatus inoperative.

The apparatus of the present invention utilizes a power source withinthe detector apparatus such as a battery, which is more dependable andout of the reach of the potential intruder. To reach it the intruderwould cause the alarm to be triggered. The apparatus of the presentinvention also utilizes the light of the installa' tion, that is,daylight when present, or the normal illuminating means during darkness.This elininates the need for the special illuminating means and cost ofoperation. Further, in the design and arrangements of the sensors of thedetector apparatus, consideration is given to the requirement of theinstallation in which the apparatus is to be used. For example, aninstallation in a residence would require certain provisions, whereas,an installation in a store building with large front windows wouldpresent problems requiring additional or different provisions.Similarly, an area such as a wharehouse and a storage area in an openyard would present different problems and the provisions of differentcharacter for their solution.

Many of these differences in requirements can be fulfilled by mereadjustment of a given piece of apparatus. Others would need be metby adifferent arrangement of the detector sensors in the apparatus, whichstill falls within the scope of the present invention.

The illustrative example of the invention used in this applicationpertains chiefly to the kind that would be used in residences, smallbusinesses, offices and the like. It can be used to sound a local alarm,or it can be connected into a monitoring system to alert a centrallylocated security force whose responsibility it is to investigate. Theinvention apparatus may be used in conjunction with other securityapparatus either to provide greater security or to serve under specialcircumstances.

One general type of sensor means would provide for detection of motionanywhere in a given area in any direction from the detector apparatus.In other words the sensor means is omnidirectional. This would find usein a large open area as in an outer office, or in an art gallery ormuseum. Another general type would be one that is directed at specificarea within a greater area, as toward a vault or safe, an access meanssuch as a door or gate. Still other uses would be in combination with atelescopic means, as a monitoring means for altering military personelto movement through a given area of enemy troop or vehicles.

As specific areas requiring different provisions are met with, they canbe satisfied, generally by one of the general types herein disclosed.This does not preclude the rearrangement of the sensors in such a manneras to satisfy the specific requirements of the new situation. Forexample, if the installation was for the detection of movement down ahall on one of the floors of a high building from which openings ledinto several offices, such installation area would be substantiallyshielded from outside interference, and the access to the area would belimited to the elevator and stairwell. Movement in the area would bemore or less restricted into a path in one or two directions from thepoint of access. By the arrangement of the sensors in the retinamovement within the area could be made to produce signals that would bytheir frequency indicate the speed of movement of the intruder, hisdirection of movement and approximately the distance that the intrudermoved down the hall. By spacing the sensors in the retina with graduallyincreasing spacing, the signal produced by movement of the intruderwould be a variation of frequency indicating the direction of movement.

The length of the pulse train would be an approximate indication of thedistance the intruder moved down the hall. Various arrangements of thesensors in the retina can be made to provide different characteristicsin the alarm for indication of the nature of the intrusion.

The electronic portion of the detector apparatus of the presentinvention is designed and arranged to selectively amplify only thosesignals which would be in the frequency range normally produced by anintruder, sneaking through the area being monitored. Other signals inthe output of the sensory means would be attenuated and not amplified tothe same extent. From the amplifier, the signals are fed to a unitizer,which produces pulses of uniform energy content for each pulse that isfed thereto from the amplifier. The threshold of the unitizer is suchthat it eliminates all the noise voltages and low amplitude signalvoltages and thus eliminates many of the causes of false alarms. In theunitizer, the amplitude of the pulses is increased and normalized as tothe amplitude and pulse width.

Following the unitizer is an energy storage means. Between the unitizerand the energy storage means is a means for regulating the rate ofcharge of the storage means. Connected to the energy storage means isalso a bleed means having a means for regulating the rate of bleed ofenergy therefrom.

The pulses produced in the unitizer would have only one variable, andthat would be the pulse rate or pulse frequency. Thus many of the falsealarms can be eliminated by the control over the charging rate and thebleed rate. The level of the energy in the storage means exerts thecontrol over the initiation of the alarm. There are at least three modesof operation that are attributed to the storage means and the bleeder.One such mode of operation would be when the bleed is completely shutoff. In this instance, the energy level in the storage means builds upwith each input pulse until the alarm is triggered. When the alarm istriggered, a bleed of the storage continues until the alarm is shut off.Another mode of operating is when there is a continual adjusted bleedfrom the storage means that requires a predetermined pulse frequency atthe output of the unitizer for the energy level to reach the triggeringlevel. Once the triggering level is reached, and additional bleed pathis opened that causes the storage to be depleated of its charge at agreater rate. The third mode of operation is where there is a continuousalarm once the triggering level is reached followed by a modulation ofthe alarm when there is continued movement. Still another mode ofoperation would be produced by bleeding the storage means at a greaterrate for all levels of storage above the trigger level and at a slowerrate at levels below the triggering level. This latter mode is termedthe anticipate mode, wherein the level of energy in the storage means ismaintained at or near the triggering level in anticipation of thearrival of another input pulse. This would then cause an instantresponse of the alarm.

The different modes of operation allow for greater selectivity in theuse of the apparatus in obtaining the response that is desired and forthe eliminating of false alarms.

The characteristic of the alarm can be determined at the option of theuser of the apparatus, by appropriate adjustment in the apparatus. Onewould be the constant sounding of the alarm after it has once beentriggered until the apparatus has been reset. Another would be where thealarm would continue to sound so long as pulses are received, but wouldbe terminated automatically after a predetermined time interval. Stillanother mode of operation of the alarm would be where it is triggeredinitially and will sound at a continuous level followed by a modulationof the pitch of the sound in response to the reception of new pulsesduring the sounding of the alarm.

Through the use of the selective amplification and the processing of thesignals, the low amplitude signals are eliminated. Signals generated dueto light from lightning discharges would have their high amplitudechopped off and their width normalized in the same manner as any otherinput pulse, but they would be limited in number and could not bythemselves cause a false alarm. Other pulses occuring at a fixedfrequency outside the frequency range of the amplifier would be tunedout completely or eliminated at the threshold of the utilizer. Thesignals caused by moving light patterns across the area being monitoredcauses signals or pulses at a different rate than those which would because by an intruder, and their pulse trains would be much shorter thanthose that would produced by an intruder moving about-in the area. Thusby the proper adjustment of the charge and discharge rates of thestorage means these signals can be differentiated to eliminated theeffectivenss of the moving light patterns to cause false alarms.

OBJECTS OF INVENTION It is an object of the invention to provide a lowcost intrusion detector system having a high degree of sensitivity andreliability;

Another object of the invention is to provide an intrusion detectorapparatus having selective adjustments to enable it to be adapted forthe variation in requirement of different installations;

Still another object is to provide an intrusion detector apparatus whichwill operate substantially as well in periods of low illumination as itwill during periods of high illumination.

Another object of the invention is to provide an intrusion detectorapparatus that has an alarm that will respond upon the initial occurenceof the intrusion with one characteristic sound or indication as forexample a continuous tone or lamp brightness and will change to anothercharacteristic while there is movement during the sounding of the alarmas for example the modulation of the alarm tone or the brightness of thelamp.

Other objects of the invention will become obvious as the disclosureproceeds in the specification in reference to the appended drawings inwhich:

DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the functionsperformed in the apparatus;

FIG. 2 is a diagram of a lens system illustrating the difference ineffect between a single and double lens system;

FIG. 3 is an elevational view, partly in section showing one embodimentof the sensor means and a light shield therefor;

FIG. 4 is an elevational view, partly in section, disclosing anotherembodiment of the sensor means;

FIG. 5 is still another view in elevation of a sensor means designed foromnidirectional sensing;

FIGS. 6A, 6B, and 6C are schematic views of different portions of theelectronic components and circuits for amplifying and processing thesensory signals;

FIG. 7 is a perspective view of the detector apparatus disclosing thecabinet and the sensor means mounted thereon; and

FIG. 8 is a partial rear view of the detector apparatus cabinetdisclosing the indicator light.

DETAILED DESCRIPTION OF INVENTION FIG. 1 of the drawing depicts thevarious functions performed in the detector apparatus in the order inwhich they are performed.

In the detector means, the changing light intensities and moving lightpatterns are converted into pulses of voltage varying in amplitude independence on changes in intensity on different portions of the sensor.Light changes over the whole area viewed by the sensor will not producevoltage changes at the output of the sensor by reason of the design ofthe circuit. On the other hand, a light pattern moving across thesensors will produce voltage differences in the sensor circuits thatresult in a train of pulses being produced at the output of the sensormeans. These pulses are coupled through the resistor means 1 to a filtermeans 2 which operates to pass pulses in a frequency rangerepresentative of the movement of the intruder but not frequencies abovethis range. Such filters provide attenuation for the higher frequenciesbut little or no attenuation for the lower frequencies. From the filter2 the signals are fed through an impedance transformer 3, wherein thechanging impedance of the detector means due to changes in illuminationof the sensor elements can be matched to the impedance of the amplifier.From the impedance matcher 3 the signal passes through another filter 4that further attenuates the higher frequencies signals. From the filter4 the signal voltages are passed through a selective amplifier 5 havinga low pass filter 6 in its feed back circuit, a filter 7 and a secondamplifier 8 having a filter in its feed back circuit at 9. Theamplifiers are selective of the signals they amplify to the extent thatthe filters in the feed back circuits attenuate the higher frequenciesof the noise voltages and thus provide an improved signal to noiseratio.

The signals from the amplifier 8 than pass through a light sensitiveattenuator 10, which is a means that responds to the ambient lightintensity of the field of view of the area monitored, to alter theresistance and voltage drop across a voltage divider, which serves an aninput to a level detector 11. The level detector 11 functions toeliminate the low amplitude noise voltages and low amplitude signalvoltages and provides for an adjustable threshold level. The low voltagenoise and low amplitude signals fail to pass and only those signals thathave amplitudes above the threshold value are amplitied and passed onthe unitizer consisting of an amplitude normalizer l3 and the pulsewidth normalizer 14. In the unitizer the pulses are reformed or producedthat have the same energy content, or are unitized. The unitizeractually responds to the output of the level detector to generate thepulses of uniform energy content, there being a pulse produced for eachamplitude peak at the output of the level detector. Any of the signalsthat are initiated by extraneous causes which escape elimination in thefilters, the selective amplifiers, and the threshold level of the inputto the level detector will appear as pulses of unit energy content inoutput of the unitizer. Here the only variables will be the frequency ofthe pulses, the length of the pulse trains, and I the space between thepulse trains.

The energy of the unitizer is fed into a storage means 15 having a meansfor controlling the rate of charge of the storage means 15 and a means16 for controlling the rate of bleed of energy from the storage means15. The level of the energy in the storage means 15 is used as a meansfor triggering the alarm means 18. Between the storage means and thealarm 18 is a switch means 17 which responds only to a predeterminedlevel of energy in the storage means. Once this level is reached theswitch means operates to initiate the alarm.

As previously mentioned, the alarm may be a continuous one until turnedoff by the user,or until it is automatically turned off after apredetermined period or one that responds to each pulse input to theswitch means. The alarm signal may also be modulated to indicate motionin the field of view after the alarm has once been triggered.

The various functions above enumerated will appear with greater clarityfrom the disclosure of the structure of the detector apparatus that nowfollows.

FIG. 2 of the drawings is a diagram illustrating the difference ineffect of one and two lens systems. On one of the lens 20 is mounted anarray of photosensors 23 called the retina.

The photoconductive cells 23 are arranged in spaced relation and affixedto the surface of the lens 20. As illustrated in FIG. 2, thephotoconductive cells are arranged in an equally spaced relation, one toanother, in a direction in which the motion of the image is expected totake place. In the arrangement, the arrow 25 represents the limit of thearea in the direction of motion in which the object or intruder isexpected to move.

When the object moves either up or down, as seen in FIG. 2, the imagewill move over the retina of cells, causing the cells to be swept bychanging light patterns, thus causing undulations of the resistance ofthe cells. If it is assumed that the speed of motion of the object isconstant in each case, it is obvious that the spacing of the cells willbe the sole factor in determining the frequency of the signal that willbe produced from the sensory means. As the spacing of the cells isincreased, the frequency of the signal would be reduced and as thespacing of the cells is is decreased, the frequency of the signal wouldbe increased. Thus in constructing the sensory means for a givenenviromental condition in which the apparatus is expected to be used,the lens means is constructed to provide the proper image size and speedof the image travel over the retina and the cells are spaced to provideproper signal frequencies.

It will be seen that the intruder will have a minimum speed of zero anda maximum speed depending on his capability. Thus, for any givenconstruction of the apparatus, the signal will have a frequency within arange of frequencies depending on the speed of the intruder. The maximumspeed of the image will be caused by the maximum speed of the intruder.The maximum frequency of the signal that is produced by the intruder canbe limited by the selection of the right spacing for the cells in theretina. Once the spacing is determined, the upper frequency of thesignal is set by the capability of the intruder.

In the construction of the apparatus for different enviroments, thechanging of the spacing of cells in the retina, changes the frequency ofthe signal, so that the same electronic apparatus may be used for a widevariation in the lens and retina structures.

The extreme of enviromental conditions would be exemplified on the onehand by an outside storage yard with its great range and area and on theother hand by a room enclosed by walls with its small range and area. Inconstructing apparatus for the two different enviroments the electronicsignal processing means would be identical. Only the lens structure andthe spacing of the cells in the retina would be different in the twopieces of apparatus.

FIG. 2 demonstrates the effect of the lens system on the retina. Withlens alone, the rays 26, 27 from the object moving parallel enter thelens 20 and are refracted but once, that is, at the point of entry ofthe lens 20. The rays 26, 27 converge and impinge on the retina 24 atpoints 28 and 29. Movement of the object 25 either up or down will causethe rays 26, 27 to move down and up relative to the retina thus causinga rather blurred image to be sweeping from one photosensor element 23 tothe next. Each time the light intensity changes on one sensor elementrelative to that on the others in the array, a volt age having anamplitude proportional to the amplitude of change in light intensity isproduced at the output of the array.

Assuming that the rays 26, 27 emanate from an object at a greaterdistance from the lens, it can be seen that the area of the retina uponwhich the rays impinge is approximately the size of the sensory elementand that the whole object would need to be moved to cause the light raysto move from one sensory element to the next, which is a requirement forthe production ofa detectable voltage difference.

On the other hand, any movement of objects smaller than the previouslyassumed object. would cause light intensities to change on differentportions of the elemental sensor element but the total illumination ofthe elemental sensor would not change or would remain substantially thesame and no voltage change at the output would be produced. Thus, foruse in detecting motion of objects of a small size at a greater distancerequires another lens means to magnify the image on the retina so thatchanges due to motion would cause changes in the light pattern to spreadover several elemental sensors in the array of the retina.

With the spherical lens 21 interposed between the field of view and thelens 20 there will be a magnification of the image of the field of viewon the retina. At the point where the rays 26, 27 impinge on and leavethe lens 21 they are illustrated by dashed lines. They converge on thefocal point of the lens 21 and diverge towards the lens 20, to berefracted on the entrance of lens 20 to impinge on the retina at points33 and 34. The mere introduction of the lens 21 into the system hasmagnified the image of the field of view to encompass substantially theentire retina that is illustrated. Two things occur in this instance,firstly, the image on the retina is brought into sharper focus,providing sharper contrasts, and secondly, the movements of elementalportions of the field of view will be detectable.

For closer fields of view, it will be seen that one lens would be allthat would be required. As fields of view are moved closer to the lens,the image on the opposite side of the lens will retreat from the lens.Also, as the image retreats from the lens it becomes larger and theimage on the retina becomes more indistinct and spreads over a greaterarea of the retina. Unlike the eye, the indistinctness of the image onthe retina is not so vital in the detection of motion. Sharpness of theimage would be productive of sharper signals which in the electronicsystem to be described would not be of much importance. More important,is the area of the retina subject to the view.

The single lens system in its unshielded installation gathers light fromall directions and even from a direction from the side that the retinais located. There is enough light gathered and impinge on the retinathrough the operation of multiple reflections within the sphere, thatmotion will be detected outside the direct field of view.

The sensors 24 may be arranged in any particular pattern on the surfaceof the sphere 20, as required by the needs of the installation in whichthe detector is to be used. FIG. 2 shows the sensors more or less evenlyspaced to form a retina that could be largely influenced by whattranspires in a field of view in a direction toward the opposite side ofthe sphere from which the sensors are located. The sensors may bearranged similar to the rod and cones of the human eye, that is withthere being a greater density of sensors to take care of the field ofview directly forward of the lens, and with the density of sensors beingdiminished gradually outward from the center of the retina, that willpick up motion off to the side, thus not depending on multiplereflections for obtaining a wider field of view.

One of the objections of relying on multiple reflections to pick upmovement outside the direct field of view, is that the light variationsare of smaller intensities and also this light produces a light curtainover the whole retina that hampers the detection of motion even in thedirect field of view.

For this reason, it is desirable from the standpoint of sensitivity, toprovide light shields for the lens system to exclude light from alldirections except from the field of view that is to be monitored. Thislifts the curtain of light from the retina, and in effect light biasesthe sensors to a different point on the response curve. The contrasts ofthe image on the retina are made sharper because of the removal of thecurtain of light and the detector system is made more sensitive assmaller changes in the light pattern are able to be detected. Thecharacter of the shielding are many and varied, and would be largelydetermined by the needs of the installation. Two examples of shield areshown in FIGS. 3 and 4.

In FIG. 3, the shielding cover 23 is arranged to limit the field of viewto a given direction from the retina thus excluding light from alldirection except from a particular field of view.

FIG. 4 shows another shield means wherein the field of view is extendedin a circumferential direction and restricted in a vertical direction,providing more omnidirectionality with less beclouding light.

FIG. 5 illustrates another embodiment of the detector means having asphere 20 on which the sensor elements are arranged in spaced relationcompletely around the lens. The top and bottem of the lens is partiallyshielded from light and providing a wider field of view in the verticaldirection. This type of detector would be suitable for installationssuch as a room where it is desired to observe movement everywhere in theroom, and where the motion would be in a horizontal plane. Thearrangement has other advantages in that motion above a certain levelwould be more or less ineffective thus making it possible to excludesome of the causes of false signals. The sensors 23 are spaced aroundthe periphery of the sphere slightly below the central horizontal planethereof. They are connected in series parallel arrangement by conductors35 which lead downward to enter the mounting support 39 at 38, 37, and36. The shielding at the top and bottom can be varied to suit therequirements of the installation.

There are a wide variation of different designs for the detector to meetthe various needs of various installations and it is intended that minormodifications of the arrangement of the sensors on the lens system andmodification of the shape and extent of the shield means be embracedwithin the invention as set forth in the appended claims.

Referring to FIG. 6A, the sensor elements 80, 81 are connected in seriesparallel array, between the source of voltage, represented by the busses82, 83.

Each sensor is a photosensitive resistor, having a serpentine deposit ofphotosensitive material upon a substrate of insulating material. The twoportions 80, 81 are connected together on the substrate and from thisconnection is led an output terminal. As used in the array, the othertwo terminals of the portions 80, 81 are connected together externallyof the substrate, to form the portions 80, 81 as parallel circuits, thusto reduce the impedance over what it would be with a series connectionof the portions 80, 81.

The retina of the sensor means is composed of these elements 80, 31,connected in series in three parallel circuits 84, 85, 86, across thesource of potential 82, 83. Each of the parallel circuits form apotential divider and as the light pattern changes on thephotoresistors, the voltage drops in the divider circuits areredistributed. The parallel circuits are connected respectively throughresistors 87, 88, 89 to a common point 79, that functions as a summingconnection, producing voltage changes at the point 79 in response tochanges in the light pattern over the entire array composing the retina.A uniform change of light intensity over the entire array will not beproductive of any change in voltage at point 79, as in that case, allparallel circuits are affected to the same degree and there would be thesame distribution of the voltage drops in each parallel circuit asbefore the change in light intensity. The change in ambient lightintensity, that is, intensity of light over the entire retina, does havethe effect of changing the source impedance or the impedance of thedetector means. The ambient light acts as a light bias, and theintensity thereof determines the operating point in the impedance range.The impedance varies from a low value for high illumination intensitiesto a high value for low illumination intensities. The range ofvariations of impedance of the individual sensors is between 52 kilohmsand I megohms. This wide range of variations is minimized to a degree bythe parallel connections of the portions 80, 81 of the individualsensors and by the parallel connection in the array itself. Thereduction in the range of impedance variations also results in areduction in the range of variation of the noise in the detector means,because the noise varies in proportion to the impedance.

The output of the retina is connected from point 79 through resistor 90and capacitor 91 to ground and from resistor 90 to the base of theimpedance transformer transistor 92.

The resistor with the capacitor 91 form a low pass filter circuit,whereby, high frequency components of the output from the retina areby-passed to ground 83, and the low frequency components are directedthrough the base-emitter circuit of the transistor 92. In such filtersthere is no sharp cutoff point, instead, the capacitor, which is thefrequency responsive element, offers decreasing amounts of impedance asthe frequency of the signal is increased. Consequently, additionalfilters are needed in the processing of the signal to eliminate thosecomponents of the signal that are of no interest.

As has been mentioned, the impedance of the source or the detector meansvaries over a wide range. The transistor 92 is connected at itscollector direct to the voltage source 82 and from its emitter throughresistor 93 to ground 83. The input impedance of the transistor 92 ishigh to match the impedance of the source of signals. The impedance ofthe output of the transistor 92 is relatively lowerfor the matching withthe input of the amplifier stage that follows. Large variations of thesource of signals impedance results in a lower variation in theimpedance of the output of the transistor 92.

The output from the transistor 92 is connected via resistor 94 andcapacitor 95 to ground, forming a second low pass filter, and throughcoupling capacitor 96 and connector to the base of transistor 102 (FIG.6B).

The busses 82 and 83 are connected across a series arrangement of asource of voltage, such as battery 99 and a potentiometer 97. Thisrepresents a means by which the voltage impressed across the detectormeans and impedance matching means may be selectively adjusted to suitthe needs of particular installations and illumination intensities.

The filters 2 and 4 on each side of the impedance transformer 3 and theimpedance transformer are mounted on the detector means or closelyadjacent thereto to obtain the best results possible.

In FIG. 6B is disclosed the two selective amplifiers 5 and 8 with a lowpass filter 7 interposed between them to add further purification of thesignal. The first selective amplifier 5 comprises of two transistors 102and 106. The base of transistor 102 is fed the input signal through thecoupling capacitor 96 (FIG. 6A) and the connector 100. Connectors 100and 101 provide a means by which different types of detector means maybe plugged into the electronic circuitry for the amplification andprocessing of the signals.

Transistor 102 has its collector connected through load resistor 104 tothe source of potential 105 and its emitter connected through biasresistor 103 to ground 83. Transistor 106 has its collector connected tothe source of potential 105 through resistor 109, and its emitterconnected through resistor 107, and a bypassing capacitor 108 to ground83. The collector of transistor 102 is connected directly to the base oftransistor 106. The collector of transistor 106 is connected through afeedback circuit having a resistor 110 and a capacitor 1 11 in parallelto the emitter of the transistor 102. The feedback circuit is a filter 6and it permits the low frequency components of the signal to be fed backto the transistor 102 and attenuates the higher frequency components ofthe signal, thus making the amplifier selective on a frequencydiscriminating basis and serve to minimize the noise voltages and thecycle components and frequencies of a higher value.

The emitter of transistor 106 is connected through resistor 112 to thebase of transistor 102. This direct current feedback serves to biastransistor 102 acting as a stabilizing means and a temperaturecompensation means. Capacitor 108 serves to by pass all alternatingcurrent voltages to ground.

The output of the first amplifier is coupled to a low pass filter 7composed of resistor 113 and capacitor 114, which is in turn connectedthrough coupling capacitor 115 to the base of transistor 116 of thesecond selective amplifier 8 including transistor 116 and transistor121. Transistor 116 has its collector connected through load resistor117 to the source of potential 105 and its emitter connected throughbias resistor 125 to ground. Transistor 121 has its collector connectedthrough load resistor 123 to the source of potential 105 and its emitterconnected through resistor 124 to ground. The collector of transistor116 is connected to the base of the transistor 121 through a low passfilter circuit 9 composed of resistors 118, 120 and capacitors 119, 122.The emitter of transistor 121 is connected through resistor 126 to thebase of transistor 119 and serves as a DC. bias circuit for thetransistor 116. A series circuit composed of resistor 127 and capacitor128 is connected in shunt across the bias resistor 124. The purpose ofthe resistor 127 is to lower the gain of. the amplifier 8.

The interstage filter9 consisting of resistors 118, 120 and capacitors119, 122 operate to prevent the high frequency components of the signalfrom being fed to the base of the transistor 121. The resistor 127,capacitor 128 operates to control the gain in the amplification of thelow frequency components of the signal.

The output from the second amplifier stage is connected throughcapacitor 130 to a voltage divider consisting of fixed resistor 131, aphoto resistor 133 and a fixed resistor 134. The point of connection 132between the resistor 131 and photoresistor 133 is connected throughconnector 140, coupling capacitor 146 to the base of transistor 147(FIG. 6C) forming the input of the level detector 11. The voltagedivider, termed automatic light sensitive attenuator 11) operates inresponse to changes in light level of the field of view of the detectorapparatus. At high levels of illumination the photoresistor 133 has alow resistance and at low levels of illuminatiomthe photoresistor 133has a high resistance. This voltage divider serves to vary the level ofthe signal fed into the level detector 11 to compensate for the excessnoise that is generated during low levels of illumination at thephotosensors. v

Connectors 1411, 141 connect the amplifiers through to the leveldetector 11, with connector 140 in the base circuit of the transistor147 and a connector 141 in the ground connection.

The busses 105, 83 are connected to a source of voltage 135 byconductors 136, 137. The arrangement of the different sources of voltagefor the different sections of the detector apparatus enables that eachsection can be supplied with the proper voltage for best operation andalso to minimize the possibility of feedback voltages through thebusses.

Referring to FIG. 6C, the input to transistor 147 constitutes the leveldetector means 11. It has its collector connected through load resistor152 to the source of potential 143 and its emitter connected throughresistor 156 to ground 83.

The collector of transistor 147 is further connected through resistor153 to the base of transistor 158, whose collector is connected throughload resistor 159 to the source of potential 143 and its emitter isconnected through the biasing resistor 156 to ground 83. The base oftransistor 158 is connected to ground 83 through resistor 155. Theresistors 152, 153, 155, form a voltage divider across the source ofvoltage 143, 83, to bias the base of transistor 158. A voltage dividerconsisting of resistor 148, potentiometer 149 and resistor 150 isconnected across the source of voltage 143, 83, and is designed toprovide a selectably adjustable source of bias voltage for the base oftransistor 147. The potentiometer 149 is connected to the base oftransistor 147 through resistor 151, whereby, the threshold of thetransistor 147 may be controlled. By use of the potentiometer, the biasmay be adjusted to such value that the transistor 147 would only respondto signals having an amplitude ofa predetermined level and above. Allother signals of lower amplitude would be ineffective in the productionof a response of transistor 147.

Transistor 147 in combination with transistor 158 constitutes a Schmidttrigger, wherein transistor 158 is normally conductive by reason of thebias on its base. During this period of conduction of transistor 158,the voltage at its collector is at its lowest value. Transistor 147 isnormally nonconductive. When a pulse of such amplitude that exceeds theadjusted threshold of the transistor 147 is transmitted to the base oftransistor 147 it becomes conductive and remains conductive for theduration of the pulse that exceeds the threshold value. When transistor147 becomes conductive, the voltage drop across resistors 152 and 156 isincreased, lowering the bias on the base of the transistor 158 andlowering the voltage across the collector-emitter of transistor 158,causing it to become nonconductive. The voltage at the collector oftransistor 158 is thus raised from the low value while transistor 158 isconductive to a value of the source 143 when the transistor becomesnonconductive.

When the input voltage to the base of transistor 147 falls below thethreshold voltage, the transistor 147 becomes nonconductive, at whichtime the voltage drop across the resistor 152 is reduced, thus raisingthe bias on the base of transistor 158 and across the resistor 156, thusincreasing the voltage across the collectoremitter of transistor 158.The transistor 158 then becomes conductive. This causes a lowering ofthe voltage at its collector to its previous low value and theproduction of a pulse of variable width but of uniform amplitude.

The output from the Schmidt trigger is a pulse that has been amplitudenormalized, that is, all pulses from the output of the Schmidt triggerwill have the same amplitude. The section is termed a Pulse Amplitudenormalizer.

The output of the pulse amplitude normalizer is connected from thecollector of transistor 158 through coupling capacitor 160 to the baseof transistor 162. The base is also connected through the resistor 161to the source of voltage 143. The collector of the transistor 162 isconnected through load resistor 164 to the source of voltage 143 and itsemitter is connected directly to ground 83.

The transistor 162, with its input circuit is a pulse width normalizer,or in other words, it produces pulses of uniform width and amplitude.

While transistor 158 and 162 are both conductive, there is a voltagedrop across the capacitor 160 in a direction from right to left, asviewed in the drawing. This causes the capacitor 160 to becomes charged.When the transistor 158 becomes nonconductive, its collector voltagejumps from its low value to that of the source 143, reversing thevoltage drop across the capacitor 160. This causes a voltage pulse ofnegative character to be transmitted to the base of the transistor 162and it then becomes nonconductive, producing a jump in the voltage onits collector and the beginning of the positive going pulse. Thetransistor 162 remains nonconductive until the capacitor 160 acquiressufficient charge in the reverse direction to raise the voltage on thebase of transistor 162 to its triggering potential. The time period isconstant, depending on the RC constant of the circuit including thecapacitor 160 and the resistor 161. When the transistor 162 again becomeconductive it collector voltage returns to it low value and the pulse iscompleted.

The combination of the Schmidt trigger and the transistor 162 producespulses of uniform amplitude and uniform width and is termed a PulseUnitizer, because, each pulse so produced will have a voltage of uniformamplitude, which causes a current to flow for a uniform length of timeand thus will have the effect of producing uniform energy pulses. Thefrequency of the pulses will depend on the rate of movement in the fieldof view of the detector means, the distance between the detector meansand the space constituting the field of view, and the spacing of thesensors in the retina of the detector means. At the output of the pulseunitizer the variable factor is the pulse frequency. In one mode ofoperation where frequency is utilized, there is also the factor oflength of pulse trains that is variable. By spacing of the sensors andproper design of the lens system, the detector can be fitted to meet theneeds of any particular installation. The frequency of the pulses, dueto movement of an intruder in the field of view, can be made to have adefinite range and to appear in a predetermined part of the frequencyspectrum. By so doing, the signals of interest as those generated by anintruder, can be separated frequencywise from those which are producedby other influences. As the signals are so separated, it becomes easierto eliminate the causes of false alarms. The length of the pulse trainscan also be used to differentiate between those signals caused by anintruder and those signals that are caused'by other influences. Forexample, a pattern of light sweeping across a detector retina due to apassing vehicle would not only produce pulses of a higher frequency thanthose produced by an intruder in the field of view, but also wouldproduce a pulse train that would be shorter than those produced by anintruder. By making the detector apparatus responsive to specificfrequencies and/or length of the pulse trains, would make the detectorexclusively responsive to an intruder.

The output of the unitizer is connected from the collector of transistor162, through a variable resistor 166, and diode 167, to one terminal ofa storage capacitor 168. The other terminal of the capacitor 168 isconnected to ground 83. Across the capacitor 168 is connected a switch169, providing means for the discharge of the capacitor 168 and as ameans for preventing the arming of the detector apparatus.

Also connected across the capacitor 168 is a bleed circuit having afixed resistor 171 and a variable resistor 172, whereby, the rate ofbleed of the charge on the capacitor 168 can be regulated. The variableresistors 166 and 172 can, if desired, be connected together forsimultaneous operation, or they may not be connected, so that they maybe separately adjusted, whereby, the energy level within the storagecapacitor can be made depending on the pulse frequency, as well as onthe length of the pulse trains.

The output of the capacitor 168 is connected through connector 175 andresistor 178 to the base of the transistor 179, which is furtherconnected through resistor 180 and capacitor 181 to ground 83. Capacitor181 prevents the capacitor 168 from bleeding to ground through thecoupling circuit.

The transistor 179 has its collector connected through load resistor 182to the source of voltage 143 and its emitter connected to ground throughresistor 183. The collector of transistor 179 is further connectedthrough resistor 184 to the base of transistor 186 and through resistor185 to ground 83. The resistors 182, 184 and 185 form a voltage divideracross the source of voltage 143, 83 and acts to provide a bias for thebase of transistor 186. The transistor 186 has its collector connectedthrough load resistor 187 to the source of voltage 143, and its emitterconnected through resistor 183 to ground. The circuit including thetransistors 179, 186 is a Schmidt trigger, which is operable as aswitch. The transistor 186, in the absence of a signal at the base oftransistor 179, will be conductive, producing a low potential on thecollector of transistor 186. When the energy level in the capacitor 168reaches a predetermined level, determined by the threshold of transistor179, transistor 179 will be triggered into conductivity. This reducesthe voltage on its collector and lowers the bias on the base oftransistor 186, so that it becomes nonconductive.

The conductivity of the transistor 179 and nonconductivity of transistor186 continues so long as the pulses of energy fed to the storagecapacitor is adequate to maintain the energy level therein above apredetermined level as determined by the threshold of the transistor179.

The collector of the transistor 186 is connected through resistor 188 tothe base of transistor 190, which has its collector connected through arelay solenoid 195 to the source 143 and its emitter connected directlyto ground 83. Transistor 190 is rendered conductive when transistor 186is nonconductive because, at that time there is no current flow in theresistor 186 and the bias voltage of the base of transistor 190 becomessubstantially that of its collector. Thus, while transistor 179conducts, the solenoid 191 is energized. The solenoid is shunted by adiode 191 to discharge the field of the solenoid 195, when thetransistor 190 ceases to conduct. The solenoid 195 creates a magneticfield that actuates the contacts 192 in the external circuit whichincludes switch 193 and terminals 194. The terminals are provided, forthe connection of the detector apparatus to an audible or visual alarmat a remote point as for example at a security guard station. It may beconnected to an automatic telephone calling system to summon the policeof the area.

Switch 193 is provided to render the external circuit inoperative as forexample when there is no need for the detector apparatus to alert thesecurity guards.

A local alarm is also provided in the form of a siren 18. A connectionfor this alarm is made to the collector of transistor 186 via conductor238, which leads through resistor 2.39 to the base of transistor 245,having its collector connected through a speaker 241 to the source ofvoltage 143 and its emitter connected to the base of transistor 240.Transistor 240 is connected with transistor 245, that is, the collectorof transistor 245 is connected to collector of transistor 240 and theemitter of transistor 245 is connected to the base of transistor 240.

The local alarm 18 comprises, in addition to transistors 245, 240, atransistor 249 having its collector connected through load resistor 256to the source of voltage 143 and its emitter connected directly toground 83. The base of transister 249 is connected through couplingcapacitor 259 to the collector of transistor 240. Also, the base oftransistor 249 is connected through resistor 258 to its collector, andits collector is connected through resistor 257 to the base oftransistor 245.

When the transistor 186 is nonconductive, the voltage of the source 143is applied through conductor 238 and resistor 239 to the base oftransistor 245. This renders transistors 240, 245 conductive and currentflows through the speaker causing a change in voltage at collectors oftransistor 240, 245. This change in voltage is coupled through thecapacitor 259 to the base of transistor 249 that renders it conductiveand creates a large voltage drop across the load resistor 256. This dropin voltage is coupled to resistor 257 and through it to the base oftransistor 245, that terminates the conductivity of transistors 245',240.As soon as capacitor 249 transfers the rise in voltage of collectorof transistor 240 to the base of transistor 249, it ceases to conductand the circuitry operates to generate an audio frequency tone in thespeaker. This occurs immediately after the alarm circuit is activatedindicating intrusion of the area or spaced being monitored.

Movement within the area or space continuing after the alarm has beenactivated, will cause modulation of the alarm or indicator signal. Forthis purpose, the unitized pulse output from the transistor 162 isconnected by conductor 246, through diode 247, resistor 248 and resistor250 to the base of transistor 249. A capacitor 251 connects this circuitto ground at a point from between resistors 248 and 250. As the pulsesare transmitted from transistor 162 to storage, they are alsotransmitted to the base of transistor 249, to modulate the output of theoscillator. So long as there is no movement in the area or spacemonitored, after the alarm has been initiated, the output of theoscillator will be a constant tone. lf movement takes place in the areaor space while the alarm is activated, the indication will be changedto'a modulated tone, or wailing sound. The sharpness of the modulationcan be altered by substitution of capacitors of different capacitancesfor the capacitor 251, or the capacitor may be eliminated.

The apparatus has several different modes of operation which can beeffected by adjustment of the controls of the detector apparatus.

For example, one mode of operation is termed the anticipate mode, whichis brought about by an automatic change in the bleed rate from thestorage means,

in response to the level of energy stored therein. There will be oneslow bleed rate for storage levels up to the level at which the alarm isactivated and a higher bleed rate for storage levels above the level atwhich the alarm is activated. The difference in bleed rates provide forinterruptions of the alarm if after continued operation of the alarm fora predetermined period there has been no additional pulses of energy fedto the storage means to maintain the storage level. After the alarmceases to be activated, the bleed rate is reduced to the rate dictatedby the setting of the potentiometer 172. This maintains the storagelevel at or near the triggering level for a longer period of time inanticipation of another pulse input. Also, it is evident that after thealarm is activated that the input of pulses to the storage means willhave to be at a greater rate to maintain the alarm activated.

This anticipate mode of operation is obtained by adjustment of thepotentiometer 172 in the bleed circuit from storage capacitor 168 to ahigh resistance setting, thus providing a slow bleed rate so long as thetransistor 179 is nonconductive. When transistor 179 becomes conductive,as has been explained, the alarm is activated. Also a new bleed path iscreated when transistor 179 becomes conductive, that is, through itsbaseemitter circuit to ground. Thus, while transistor 179 conducts, andwhile the alarm is activated, the bleed rate is increased by theaddition of the new bleed path. As soon as transistor 179 ceases toconduct, the bleed rate then is determined by the setting of thepotentiometer 172.

Another mode of operation is controlled by switch 220 connected in acircuit between collector of transistor 186 and the base of transistor179, which includes resistors 221, 180, and capacitor 181. This istermed the latch mode. With the switch 220 closed and when the level ofenergy in the storage capacitor reaches the point where transistor 179becomes conductive, the transistor 186 ceases to conduct and the alarmis activated. The rise in voltage at the collector of transistor 186 istransmitted through switch 220 and resistors 221, 180 to the base oftransistor 179, thus maintaining its conductivity and the continualsounding of the alarm. In this instance it makes no difference whetherthere is other pulses fed to the storage means or not, the alarm willcontinue to be activated until the switch 220 is again opened. It ispossible, during the latch mode, for the alarm, particularly, the localalarm, to be modulated by movement of the intruder within the monitoredarea.

For the purpose of delaying the arming of the detector apparatus orrendering it ineffective for a short period after it is turned on, ameans is provided for grounding the electronic system to prevent thesignals during that that period from activating the alarm.

Since the apparatus contains it own power supply and all the controlstherefor, it is essential that the arming of the apparatus be delayedfor a period necessary to allow the attendant to escape from the areabeing monitored. For this purpose, a transistor 206 is provided as aswitch means for connecting the base of transistor 147 to ground whentransistor 206 is rendered conductive. Transistor 106 has its collectorconnected to the base of transistor 147 by conductor 209 and its emitterconnected to ground by conductor 208. The base of transistor 206 isconnected through resistor 207 to the junction 204 in a voltage dividercontaining capacitor 200, and resistors 202 and 203. The capacitor 200is shunted by a switch 201, which when closed provides a continual flowof current through the resistors 202 and 203. This produces a voltage atpoint 104, which when applied to the base of the transistor 206 willtrigger it into action. When it is triggered into action, the base ofthe transistor 147 becomes grounded, thus preventing signals from beingtransmitted beyond the transistor 147. The apparatus is then in thedisarmed mode. The apparatus will remain in the disarmed mode until theswitch 201 is again opened and remains disarmed until the capacitor 200becomes charged, thus returning the voltage at the base of thetransistor 206 to ground potential.

The closing of switch 169, which shunts the capacitor 168 will preventthe build up of the energy level in the capacitor and also function torender the apparatus inoperative or disarmed. I

The transistors 212, 213 have their collectors connected through a lamp214 to the source of voltage 143. The transistor 212 has its emitterconnected to the base of transistor 213 and the emitter of transistor213 connected to ground 83. The base of transistor 212 is connectedthrough resistor 210 to the junction 211 between capacitor 200 and theresistor 202. This circuitry is merely an indicator of the arming. Whilethe switch 201 is closed the base of the transistor 212 is connected tothe source of voltage and it with the transistor 213 is renderedconductive, causing the lamp 214 to light up to its full brilliance,indicating that the apparatus is in the disarmed mode. When switch 210is opened the lamp 214 remains lightedbut the brilliance thereofdecreases with the charging of the capacitor 200 until, the voltage atthe base of the transistor 212 is reduced to close to ground potential.At that time the lamp 214 is extinguished and the apparatus is thenindicated as being armed.

The base of the transistor 206 is also connected through resistor 263switches 262, 261 to the collector of transistor 186. This circuit isprovided for installations wherein there may be large megnetic fields,that might induce voltages in the circuit of the detector apparatus,that would cause the alarm to continue to be activated when once it hasbeen activated. Closure of the switch will apply the collector voltageof the transistor 186 to the base of the transistor 206 to ground thebase of the transistor 147 and silence the alarm.

The connectors 175, 176, 177 are shown in lieu of lines to connect thetwo sections of the electronic circuit that had to be displaced on thesheet of drawing. They are not in the circuitry of the actual structure.

Referring to FIGS. 7 and 8, there is disclosed the cabinet 60 in whichthe detector apparatus is housed and upon which an unshielded detectormeans 63 having a retina of photosensors 64 is mounted. The cabinet hasa console front upon which are mounted the controls, the local alarm orspeaker and the terminal receptacle for connecting the apparatus to aremote alarm or indicator.

The switch operators 65, 66, and 67 are respectively associated with thelatch switch 220, the delay arming switch 201 and the remote alarmswitch 193. The knob 68 represents the actuator for the bleed controlpotentiometer 172. The bleed control potentiometer 172 and the chargingcontrol potentiometer 166 are represented by broken line 173 as beingconnected together for simultaneous operation. If desired, a separatecontrol knob may be provided for each of the potentiometers. Switch 261is illustrated as being connected to switch 220 for simultaneousoperation. When switch 220 is closed, switch 261 is opened. Switch 262has no means external of the cabinet for its control. The speaker oralarm means is located beneath the apertures 69 where through the soundcan escape from the interior of the cabinet. The remote alarm circuit,not shown, may be connected to the recepticle 70. On the back side ofthe cabinet FIG. 8, is mounted the glass lens 72 for the lamp 214 of thearming indicator.

Various other configurations of the cabinet and arrangement of thecontrols may be made without departing from the spirit of the invention.

The present apparatus as described in the specification and shown in thedrawings has many and varied applications from that of use in aresidence to detect intruders to the use in business houses, offices,wharehouses, storage yards museums and art galleries. Variation instructure to accomodate the apparatus to the requirements of the variousinstallations may be made without departing from the spirit of theinvention as defined by the appended claims.

What l consider to be my invention is set forth in the following claims.

I claim:

1. A method of detecting motion within a predeter mined space comprisingthe steps of:

projecting a light pattern of said space;

sensing the changes in said light pattern caused by movement within saidspace to produce electrical signals in response to said changes, saidsignals having a frequency below a predetermined frequency level;

attenuating signals having a frequency above said predeterminedfrequency level;

eliminating those signals below the predetermined frequency level havingan amplitude below a certain predetermined level;

amplifying those signals below the predetermined frequency level havingan amplitude above said predetermined level producing a voltage pulse ofuniform energy content for each excursion of the amplified signals abovesaid predetermined amplitude level;

storing said pulses of uniform energy content to produce a voltage levelindicative of the level of energy in storage;

bleeding energy from storage at a uniform predetermined rate, wherebythe voltage level produced is rendered indicative of the rate of pulsesfed into storage and producing an indication when said voltage levelexceeds a predetermined level, whereby to indicate that the lightpattern has been changed by movement of an intruder in said space.

2. Apparatus for detecting motion within a predetermined spacecomprising in combination:

lens means for projecting a light pattern of said space;

retina means comprising of spaced photoconductive cells mounted on saidlens means for detecting changes in said light pattern due to motionwithin said space, the spacing of said photoconductive cells beingarranged to produce electrical signals having a predetermined frequencyin response to the maximum expected rate of motion of an object in thespace;

attenuating means for attenuating all other signals having a frequencyabove the predetermined maximum frequency;

a selective amplifier means for amplifying the signals below saidpredetermined maximum frequency;

a level detector means to eliminate low amplitude signals and voltagesbelow a predetermined level and for amplifying signals having anamplitude above said predetermined level;

pulse producing means responsive to the output of said detector forproducing pulses having uniform energy content;

storage means for receiving said pulses of uniform energy content andfor producing a voltage indicative of the number of pulses storedtherein;

bleed means for bleeding energy from said storage means at a selectivepredetermined rate, whereby the voltage of said storage means isrendered indicative of the rate of pulses fed into said storage means;

switch means responsive to a predetermined voltage level at the outputof said storage means; and

alarm circuit including said switch means having an indicator forindicating when movement takes place in said predetermined space.

3. Apparatus as set forth in claim 2 wherein said indicator comprises;

an audio alarm system initiated by said switch means;

and

means responsive to the pulses fromsaid pulse producing means, tomodulate said audio alarm system at a rate depending on the rate ofpulses produced by said pulse producing means.

4. The apparatus as set forth in claim 2, further in- 20 cluding:

means activated when said switch means responds to the level of voltageat the output of said storage means for providing an additional bleedpath to increase the rate of bleed from said storage means while theswitch means is activated.

5. The apparatus as set forth in claim 3, wherein said alarm system isan oscillator for producing an audio frequency tone and wherein saidmeans responsive to pulses produced in said pulse producer is a sourceof modulating voltages for modulating the output of said oscillator.

6. The apparatus as set forth in claim 2, further including;

a light shield means for partially enclosing said lens means forrestricting the space viewed by said lens system to reduce the lightlevel on said retina to that in the image of the space for providing agreater contrast in said light pattern on said retina.

7. The apparatus as set forth in claim 2, wherein said lens comprises;

a sphere; and

said retina comprises photoconductive cells near the equator of saidsphere to provide for omnidirectional viewing of the space about saiddetector apparatus.

8. Apparatus as set forth in claim 2 wherein the retina comprises;

a plurality of photoconductive cells arranged in spaced relation to eachother, and wherein the spacing is increased in a direction outwardlyfrom a central part of the retina to provide for a change in frequencyof the electrical signals in response to direction of change of thelight pattern on said ret- Ina.

1. A method of detecting motion within a predetermined space comprisingthe steps of: projecting a light pattern of said space; sensing thechanges in said light pattern caused by movement within said space toproduce electrical signals in response to said changes, said signalshaving a frequency below a predetermined frequency level; attenuatingsignals having a frequency above said predetermined frequency level;eliminating those signals below the predetermined frequency level havingan amplitude below a certain predetermined level; amplifying thosesignals below the predetermined frequency level having an amplitudeabove said predetermined level producing a voltage pulse of uniformenergy content for each excursion of the amplified signals above saidpredetermined amplitude level; storing said pulses of uniform energycontent to produce a voltage level indicative of the level of energy instorage; bleeding energy from storage at a uniform predetermined rate,whereby the voltage level produced is rendered indicative of the rate ofpulses fed into storage and producing an indication when said voltagelevel exceeds a predetermined level, whereby to indicate that the lightpattern has been changed by movement of an intruder in said space. 2.Apparatus for detecting motion within a predetermined space comprisingin combination: lens means for projecting a light pattern of said space;retina means comprising of spaced photoconductive cells mounted on saidlens means for detecting changes in said light pattern due to motionwithin said space, the spacing of said photoconductive cells beingarranged to produce electrical signals having a predetermined frequencyin response to the maximum expected rate of motion of an object in thespace; attenuating means for attenuating all other signals having afrequency above the predetermined maximum frequency; a selectiveamplifier means for amplifying the signals below said predeterminedmaximum frequency; a level detector means to eliminate low amplitudesignals and voltages below a predetermined level and for amplifyingsignals having an amplitude above said predetermined level; pulseproducing means responsive to the output of said detector for producingpulses having uniform enerGy content; storage means for receiving saidpulses of uniform energy content and for producing a voltage indicativeof the number of pulses stored therein; bleed means for bleeding energyfrom said storage means at a selective predetermined rate, whereby thevoltage of said storage means is rendered indicative of the rate ofpulses fed into said storage means; switch means responsive to apredetermined voltage level at the output of said storage means; andalarm circuit including said switch means having an indicator forindicating when movement takes place in said predetermined space. 3.Apparatus as set forth in claim 2 wherein said indicator comprises; anaudio alarm system initiated by said switch means; and means responsiveto the pulses from said pulse producing means, to modulate said audioalarm system at a rate depending on the rate of pulses produced by saidpulse producing means.
 4. The apparatus as set forth in claim 2, furtherincluding: means activated when said switch means responds to the levelof voltage at the output of said storage means for providing anadditional bleed path to increase the rate of bleed from said storagemeans while the switch means is activated.
 5. The apparatus as set forthin claim 3, wherein said alarm system is an oscillator for producing anaudio frequency tone and wherein said means responsive to pulsesproduced in said pulse producer is a source of modulating voltages formodulating the output of said oscillator.
 6. The apparatus as set forthin claim 2, further including; a light shield means for partiallyenclosing said lens means for restricting the space viewed by said lenssystem to reduce the light level on said retina to that in the image ofthe space for providing a greater contrast in said light pattern on saidretina.
 7. The apparatus as set forth in claim 2, wherein said lenscomprises; a sphere; and said retina comprises photoconductive cellsnear the equator of said sphere to provide for omnidirectional viewingof the space about said detector apparatus.
 8. Apparatus as set forth inclaim 2 wherein the retina comprises; a plurality of photoconductivecells arranged in spaced relation to each other, and wherein the spacingis increased in a direction outwardly from a central part of the retinato provide for a change in frequency of the electrical signals inresponse to direction of change of the light pattern on said retina.